I want to bild a subwoofer filter?

Question

I imagine it might be just a simple condensator, but I'm interested in the details. how does the circuit look like?
is normally the top tolerated frequency about 100 Hz?

Answer 1

A passive low pass filter for a subwoofer is usually a series inductance with a capacitor in parallel with the loudspeaker.

The filter's corner frequency should be chosen with regard to the 'speaker's frequency response.